Degree of interocular synchrony required for maintenance of binocularity in kitten's visual cortex.

1. The importance of synchronous activation in maintaining cortical binocularity was studied physiologically in kittens that had been reared under different regimens of alternating monocular deprivation. 2. Three different techniques were employed to provide alternate monocular stimulation: a) mechanical shutters placed before the animals' eyes; b) goggles fitted with complementary colored cutoff filters, which restricted visual input to one eye at a time; and c) two rotating gratings that were 90 degrees out of phase. In the third technique, the gratings were always orthogonal to one another and viewed separately through cutoff filters. This allowed us to exploit the orientation selectivity of cortical cells and thereby stimulate them alternately through each eye without simultaneously affecting activity in the dorsal lateral geniculate nucleus (dLGN). 3. We based our conclusions on a sample of 691 neurons, which we recorded in 21 animals. Results with all techniques were remarkably consistent. Binocular cortical inputs predominated at normal or nearly normal levels, even when a number of seconds elapsed between successive exposures of each eye. 4. An interonset interval of at least 10 s was required to make a substantial reduction in binocularity. This interval can be separated into two parts--the duration of exclusive monocular stimulation and the time when neither channel receives input. Of these, the latter appeared to be less important. Blanking times of 0.15--1.0 s did not affect binocularity if the interonset interval was 1 or 10 s; and in one experiment where the blanking time was 9 s, the resulting disruption in binocularity was less than that found with shorter blanking times and the same interonset interval. 5. Our results imply that mechanisms responsible for the disappearance of binocular cortical inputs require independent stimulation of each eye for periods of at least a few seconds; this stimulation must be of a kind that is known to excite cortical cells. Our results with the rotating grafting show, in addition, that the mechanisms whose timing we have measured are intrinsic to the cortex.     

Neurologic complications of a coral snake bite

A 27-year-old man was bitten by a coral snake in Mexico. Within 24 hours he had ptosis, dysphonia, difficulty chewing, and limb weakness. His symptoms peaked at 72 hours with loss of ambulation. Neurologic examination was consistent with severe myasthenia. Repetitive stimulation of the median nerve showed a postsynaptic defect that was not corrected by edrophonium. He was monitored in an intensive care unit, but received no antivenom globulin or acetylcholinesterase inhibitors. The syndrome abated in 3 weeks.     

Improved use of tapetal reflection for eye-position monitoring.

A new technique is described for eye-position monitoring in species with strong tapetal reflections. A fiber optic is used to introduce light into the eye, whose optics then produce an image of the fundus on a tangent in front of the animal. The technique simplifies heretofore tedious measurement of cylotorsional changes, as well as providing a very wide view of the fundus. It has been used successfully in conjunction with single-unit recording from the visual system.     

A bitewing radiographic study of a population of diabetic and nondiabetic rhesus monkeys

A population of 7 diabetic and 13 nondiabetic rhesus monkeys (Macacca mulatta) were examined radiographically using bitewing imaging techniques. Each subject was scored radiographically for bone levels, periodontal ligament (PDL) widening, radiographic calculus, and carious lesions. Prior to examinations blood samples were obtained for fasting blood glucose levels. Results indicated that all clinical variables were generally greater for the diabetic group, with bone loss being the only statistically significant parameter. Calculus levels, however, were found to be greater radiographically in the nondiabetic group. In viewing the study population as a single group of 20 monkeys, decreased bone levels were found to be positively correlated with PDL widening and blood glucose levels suggesting an association of hyperglycemic states with possible decreased resistance to infection. It was concluded that carbohydrate intolerance with hyperglycemia in diabetes mellitus may be associated with the radiographic variable of increased bone resorption using an objective system of measurement for evaluation and scoring. Without a quantitative system of measurement such as devised in this study, other radiographic variables such as PDL widening, calculus deposits, and carious lesions may not be accurately tested against one another or correlated with other experimental clinical parameters.